The cooling systems of nuclear reactors tend to become coated with various radioactive deposits. While these deposits are not thick enough to plug the cooling systems, they do present a radiation hazard to personnel who must perform maintenance and repair work on them, Thus, it is necessary to remove the deposits in order to reduce the radioactivity to a level that is safe for personnel in the area. The deposits are conventionally removed by circulating through the cooling system a decontamination solution which solubilizes metal ions, and an oxidizing solution which oxidizes insoluble chromium oxides to the soluble dichromate ion. A typical decontamination solution consists of citric acid, oxalic acid, and a chelate, such as ethylenediaminetetraacetic acid (EDTA). A typical oxidizing solution consists of an alkali metal hydroxide and a permanganate.
Recently, it has been discovered (see U.S. Pat. No. 4,287,002) that ozone can be used as the oxidizer. Ozone offers several advantages over the alkali-permanganate in that it decomposes into oxygen and does not leave any ions remaining in the system, in addition to being an excellent oxidant. However, there are several disadvantages in using ozone as well, the principal one being its instability. This means that if the ozone must travel through a rather long cooling system, most of it will decompose before it reaches the end of the cooling system and the deposits in those portions of the cooling system will be insufficiently oxidized and will not be adequately removed.